Automatic fogging apparatus



United States Patent [72] Inventors RusselIR.Curtis Indianapolis; James E. Jung, Noblesville, Ind. [21] AppLNo. 708,195 [22] Filed Feh.26, 1968 [45] Patented Dec. 15,1970 [73] Assignee Curtis Dyna-ProductsCorporation Westlleld, Ind. a corporation of Ohio [54] AUTOMATIC FOGGING APPARATUS Primary Examiner.loseph V. Truhe Assistant Examiner-Peter W. Gowdey Attorney-Woodard, Weikart, Emhardt & Naughton ABSTRACT: A plastic housing with reservoir for liquid insecticide and an electric pump forces the liquid from the reservoir through a heat exchanger to a nozzle. A fan driven by the pump motor produces a cooling air flow through the housing and around the heat exchanger for discharge through an apertured plate. A normally closed thermostatically operated switch keeps electrical heating elements in the heat exchanger continuously energized unless excessive temperature opens the switch. A normally open thermostatically operated switch, disposed in the path of air flow through the housing and mounted to the heat exchanger for sensing the temperature thereof to close the switch and operate the pump and fan for discharge of insecticide from the nozzle, is also responsive to air flow caused by fan operation and terminates pump and fan operation before excessive cooling by liquid pumped to the heat exchanger. Heat exchanger variations facilitate disassembly and maintenance of high efliciency.

PATENTED 115m 519m 3.548151 SHEET 1 BF 2 YNVENTOR S Russsu. R.Cunr:s

By JAME E. U'uua IITTORNEYS PATENTEU DEM 5197B SHEET 2 BF 2 mvsmons Aussz LL R. CUR TIS BY AMEs E. J'u/va j/mwl WMWHW ATTORNEYS AUTOMATIC FOGGING APPARATUS background of the invention 1 1. Field of the Invention This invention relates generally to fogging apparatus and more particularly to apparatus capable of automatic production of fog using materials requiring heating.

2. Description of the Prior Art. 7

Examples of fog-producing apparatus of the prior art are disclosed in the following U.S. -Pat.: Stagner, No. 2,576,976, Dec. 4, 1951; Stagner, No. 2,615,215, Oct. 28, l952,'1-lession No. 3,200,535,Aug. 17, 19.65. 7

Problems of prior art apparatus are significant. For example, certain insecticides and other liquids which are used therein form deposits in the heat exchangers, which can 'eventually cause severe restriction or complete obstruction to liquid flow. Typical prior'art devices have been quite difficult to clean.

To provide an effective fog, goodteinperature control is necessary. Yet a typical problem of prior art devices is a wide operating temperature differential, resulting in a fog which is either excessively dry or excessively moist. Electrical supply line voltage variations have also caused substantial problems in temperature control. The pump outputremains nearly constant for supply line voltage variations. However, the power to the heating elements of the heat exchanger varies significantly with supply line voltage variation. This variation requires that the pump operate only when the heat exchanger temperature is within the required temperature limits.

SUMMARY OF THE INVENTION In a typical embodiment of the present invention, the apand out to atmosphere through a nozzle. The motor also drives a fan to establish an air flow through the housing pass the heat exchanger and out in the direction of discharge from the nozzle. A normally open thermostat is mounted to the heat exchanger and in the air flow path through the housing. It is operable, when heated by heat transfer from the heat exchanger, to close the motor circuit and start the fan and pump operation. Being disposed in the air flow caused by the fan, the thermostat dissipates heat both to'the air and to the heat exchanger during passage of liquid through the heat exchanger, so that the thermostat cools rapidly enough to terminate pump operation prior to excessive cooling of the heat exchanger. However the heat dissipation to air is minimized while the fan is off, to enable the thermostat temperature to rise with heat exchanger temperature. Accordingly, close control of heat exchanger temperature and, hence, fog quality is obtained and is maintained in spite of variations in heating rates which might result from variations of line voltage applied to the electrical heating elements in the heat exchanger.

BRIEF DESCRIPTION OF THE DRAWING FIG. 8 is a plan view of the liquid passageway plate of the LII The full nature of the invention will be understood from the accompanying drawings and the following description and claims.

FIG. 1 is an elevational view of an automatic fogging apparatus according to a typical embodiment of the invention, the view being partially in section takenon a vertical plane through the center of the apparatus. 1

FIG. 2 is a front elevational view of the fog discharge end thereof. v

FIG. 3 is an enlarged vertical section through the pump and relief valve assembly.

FIG. 4 is a schematic electrical diagram of the apparatus.

FIG. 5 is an enlarged elevational view of the thermostat assembly-formotor control. I a

FIG. 5A is a fragmentary sectional view showing the mounting for the thermostat assembly.

FIG. 6 is a plan view of another embodiment of heat exchanger. 5

FIG. 7 is a side view of the embodiment of FIG. 6.

heat exchanger of FIGS. 6 and 7. 7

FIG. 9 is a side view of an optional construction wherein the passageway plate is sandwiched between two heater castings.

FIG. 10 is a plan view of a still furthervariation of the heat exchanger.

FIG. 11 is a cross section therethrough taken at line 11-11 in FIG. 10 and viewed in the direction of the arrows.

FIG. 12 is a plan view of the back plate thereof viewed in the direction of the arrows 12-12 in FIG. 11.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings in detail, and particularly to FIG. I, the fogger is provided with a housing ll-which may typically be made of plastic molded in halves assembled together to complete the housing. In the illustrated example, one half of the housing is shown in vertical section immediately adjacent the parting face. The housing provides an integral handle portion 12 with the operating switch slot 13 therein and the reservoir receiver 14 at the bottom. The opening 16 between the handle portion 12 and the main body of the housing accommodates the fingers for convenient portability of the device.

In this example, the reservoir is provided by a cylindrical container 17 threadedly receivedat 18 in housing portion 14 and containing a supply of liquid 19. The flat bottom 21 of the container provides convenient support for the apparatus whereby it can be placed on the ground or any other convenient supporting surface.

A pump assembly 22 is mounted to the housing and projects into the container 17. An electric motor 23 is mounted in the housing and may have an eccentric mounted to its output shaft for reciprocating the pump rod 24. The motor also has a fan 26 connected to its output shaft for drawing air into the housing through a plurality of apertures 27 and establishing an air flow through the housing in the direction of the arrow 28 for discharge through a perforated plate 29, better shown in FIG. 2.

A heat exchanger 31 is also mounted in the housing and has an inlet 32 receiving liquid pumped from the container 17, and an outlet nozzle 33. Thumb screws 34 at thefront end of the housing enable removal of the noule and a portion of the heat exchanger for cleaning when desired. the heat exchanger is provided with internal electrical heatingelements which are energized continuouslythrough an open-on-temperature-rise thermostatically operated electrical switch 36 mounted to the heat exchanger. While thermostat 36'is normally closed and virtually unaffected by air flow through the housing, a second thermostatically operated switch 38 is provided and is exposed in the air path through the housing to facilitate heat dissipation to the air during fan operation. This thermostat is reverseacting (closes on temperature rise) and is mounted to the heat exchanger in good thermal conduction relation therewith.

Referring now to the schematic diagram of FIG. 4, electrical supply plug 41 is provided to supply energy through conductor 42 and the handle-mounted off-on switch 43 and thermostatically operated normally closed switch 36 to the heating elements 44 in the heat exchanger. Energy'is supplied to the motor 23 through the normally open thermostatically operated switch 38 when the temperature therein rises to .a point sufficient to close the switch.

As better shown in FIG. 5, the switch assembly 38 includes the bimetal strip 46, contact springs 47 and 48, adjustment screw mount 49 and terminal strips 51 and 52, all mounted together with spacers 53 in the stack. Suitable screws are provided in the terminal strips for connecting leads and the adjusting screw 54 is mounted on the support 49 whereby rotation of the screw moves the finger 56 linearly, operating on the spring 47 to adjust spacing between the contacts. The finger or abutment 57 mounted at the free end of the bimetal strip 46 operates on the contact spring 48 to close and open the contacts in response to the temperature of the bimetal strip. The

shown in FIG. 5A. The bifurcated clamp plate 55 overlies the stacked switch assembly 38 and is drawn down tightly by the screws 50 which are threaded into bosses formed on the heat exchanger body 31. A spacer 58, formed of a material having good thermal conductivity such as aluminum, underlies the switch assembly and facilitates thermal conduction from the body 31 to the switch assembly. The mounting arrangement is such that the switch assembly iswell exposed to the flow of air moving pass the assembly, but relatively good thermal conductivity between the switch assembly and'the body 31 is maintained.

' In the operation of the invention thus far described, a suitable supply of liquid insecticide or other material to be vaporized is provided at 19 in the container 17. The heating elements 44 are energized upon closure of the switch 43 by "operation of the handle-mounted switch button 59. As the heat exchanger temperature rises, heat transfer to the bimetal strip moves it in the direction of the arrow 61 (FIG. 5) and, at a temperature determined by the setting of the adjustment 'screw 54, the contacts close and energize motor 23. The

inotor thereupon pumps liquid from the reservoir up through the tube .62 and into the heat exchanger, through the heat exchanger and discharges it through the nozzle 33. Simultaneously the fan 26 establishes an air flow through the housing in the direction of arrow 28. Oil will continue to be pumped through the heat exchanger and will receive heat from the heat exchanger body, the thermal input to the body being provided by heaters 44. The capacity of pump 22 is sufficiently ture of theliquid at the nozzle 33 will, therefore, decrease and the fog produced will tend to become wetter. The drop in temperature of the heat exchanger body will also, however, lower the temperature of the thermostat 38, and because the heat exchanger temperature drops with continued operation of the pump, the fog produced will be driest when the pump first comes on. As operation continues the-fog becomes wetter until the thermostat 38 opens and the pump shuts off. To insure that the fog is always above an acceptable limit of wetness, the pump must be shut off by the thermostat 38 before the fog quality drops below this acceptable limit. The range of fog quality over an operating cycle is determined by the temperatures at which the pump is started and stopped by the thermostat 38. In prior artdevices, this operating temperature range might be held to a narrow value at a given voltage, but as the supply voltage varied, the operating temperature range changed. This phenomena, in prior art devices, is primarily due to the temperature lag between the heat exchanger and the heat sensing device. When high input voltage variation is encountered, and the cooling rate of the heat exchanger is low, then the thermal lag is small. But when low input voltage variation is encountered and the heat exchanger cooling rate is high then, in prior art devices, the lag is large, allowing the fog to become wet before the temperature sensing device reacts stopping the pump.

By using an open bimetal thermostatand passing cooling air over it during pump operation (that is, during the contactsclosed portion of the thermostat cycle) the control arrangement of the present invention holds the temperature differential between the heat exchanger and the thermostat to a minimum over a wide range of input voltagevariations. Since the thermostat opens and closes at preset temperatures it is imperative that the. temperature differential between the heat exchanger and the thermostat be a minimum to have effective control over the oildischarge temperature. In order to attain this desirable sensitivity, the temperature lag (thermal inertia) betweenthe two must be minimized. The arrangement of the present invention achieves this by exposing the thermostat38 to cooling air which passes over it only when the pump is operating.

rate of the heat exchanger is low, the cooling air keeps the thermostat temperature at, or slightly below, the heat exchanger temperature. If the cooling rate of the thermostat equals the cooling rate of the heat exchanger, then their temperatures will be equal. But, if the cooling rate of the thermo' stat is highest, then the heat exchanger will supply heat to the thermostat, holding the temperature differential between the two to a minimum. 1

When low input voltage is encountered and the cooling rate of the heat exchanger is maximum, then the cooling air keeps the thermostat temperature at, or slightly above, the heat exchanger temperature and the thermostat is cooled both by the air and the cooler heat exchanger, again holding the temperature differential between them to a minimum.

If the liquid is such as to form deposits when heated in the heat exchanger, and if these are allowed to accumulate without attention, it is possible that eventually the nozzle would become blocked or heat exchanger passageways excessively restrictedor blocked. The thermostatswitch 36 is adjusted so that if such blockage or restriction does occur, the temperature rise of the heat exchanger and liquid therein will be limited, because the switch 36 will open at the desired safety limit of rtemperature and deenergizethe heating elements.

To avoid pump or motor damage in the event of blockage or restriction, pump relief means are provided as best shown in FIG. 3. During normal operation, the pump piston 63 draws liquid from the container through the inlets 64 and ball check valve 66. On the pressure stroke the liquid is discharged through the spring-loaded ball check valve 67 and discharge pipe 62. In the event there is excessive restriction to discharge through the pipe 62, the rising pump pressure in the chamber 68 will be transmitted through the passageway 69 to the spring-loaded relief ball check valve 71 which will then be opened and discharge liquid to the container through the relief port 72. Overloading of the pump and-motor is thereby avoided.

An important advantage of the invention as described to this point is the fact that it provides automatic compensation for line voltage changes as previously described. The operating differential of the motor control thermostat can be minimized permitting the liquid temperature in the heat exchanger to be stabilized and held at-the temperature desired for most efficient fog generation and most effective fog particle size. The mounting of the thermostat 38 near the-discharge end of the heat exchanger avoids excessive sensitivity to incoming liquid temperature, while maintaining good control of discharge temperature.

It was mentioned above that some liquids, when heated, produce deposits inside the heat exchanger. For example, some of the oils used in insecticides deposit a carbon film on the interior of the heat exchanger. In order to avoid damage which could result from failure to maintain cleanliness in the interior passageway of a heat exchanger, thepressure relief and heater shutoff means described above have been employed. To minimize the need for operation of these safety devices, heat exchangers having minimum susceptibility to restriction by deposits, and maximum facility of maintenance, are desirable. FIGS. 6 through 8 provide an example of such a heat exchanger wherein a heater casting 76 and back plate 77 are bolted together with a passage plate 78 sandwiched therebetween. The heater-casting may bean aluminum die casting with the electrical heater element 79 cast therein and a fitting 81 thereon to receive the liquid and a nozzle 82 thereon for discharge of the heated liquid. The inlet and outlet fittings 81 and 82 communicate through the heater casting to opposite ends 83 and 84 of a serpentinepassageway 86 which may be blanked (as shown) or embossed inthe passage plate 78. Comparison of FIGS. 7 and 8 reveals thatthe passage is rather wide (X dimension) compared to the thickness of the plate (Y dimension). Also the passageway is quitelong from one end thereof to the other. This combination of features provides maximum liquid exposure to heated surfaces in a minimum of time. The provision of the liquid passages that are substantially wider than deep also means that comparatively little area is provided in the passage plate for accumulation of a film whereas the area on the surfaces of the heater casting and back plate facing each other through'the passages are comparatively large. This facilitates removal of the bulk of the deposits by simply disassembling the back plate from the heater casting and cleaning the flat faces thereof. This can be readily and quickly accomplished. a a

FIG. 9 illustrates a variation of the embodiment of FIGS. 6 through 8 wherein the heater casting 76 and passage plate 78 can be the same but an additional heater casting 87 is provided in place of the back plate. The resistance heater 88 in heater casting 87 may be cast in place the same as heating element 79 in heater casting 76. The passage plate can be made of a soft material having a high thennal conductivity so that in both examples it serves not only asa good heat conducting element but also as a seal.

FIGS. 10 through 12 illustrate another embodiment of the heat exchanger. in this example, the heat exchanger includes a heater casting 89 with resistance heater 91 cast in place. The plate 92 may be a casting with the spiral passage 93 cast or machined therein, or it may be a machined plate with the passage machined therein, for example-A passage or passages may also be provided in the heater casting if desired. The plate 92 is rigidly attached to the heater casting as in the previous examples by screws 93.

Liquid can be forced into the passage through an inlet fitting 94 threadedly received in the plate 92 and moves outwardly from the entrance 96 in the passageway to the discharge endof the passageway at 97 for discharge through nozzle 98. The heated liquid forced through the nozzle immediately evaporates and then condenses forming a fog as it mixes with the cooler air.

it should be recognized that various shapes other than those shown in the drawing can be employed. While the invention has been disclosed and described in some detail in the drawings and foregoing description, they are to be considered as illustrative and not restrictive in character, as other modifications may readily suggest themselves to persons skilled in this art and within the broad scope of the invention.

We claim:

1. In a fogging apparatus having a housing, a source of liquid to be dispensed, a heat exchanger having an inlet coupled to said source and an outlet coupled to a dispenser, a fan for inducing air flow through said housing,-and a pump for moving liquid from said source through said heat exchanger to said dispenser, the improvement comprising:

thermostat means exposed to the air flow through the housing and coupled to said heat exchanger for sensing the temperature thereof and for controlling the operation of both said pump and said fan, said thermostat being responsive to changes in temperature of said heat exchanger caused by changes in temperature of the said liquid in said heat exchanger; andsaid thermostat means being adapted to facilitate heat transfer both between said heat exchanger and said thermostat means and between said thennostat means and the air flowing through said housing during decrease of temperature of said heat exchanger. 2. The invention of claim 1 wherein: said thermostat means includes a thermally deformable member mounted on said heat exchanger, and extending adjacent thereto facilitating heat transmission therebetween, said member having a substantial portion thereof disposed in the air flow provided by said fan means during operation of said fan means to facilitate heat transmission from said member to the flowing air during fan operation.

3. In an electric fogging apparatus comprising a housing, means connected to said housing defining a reservoir for holding liquid to be vaporized and dispensed, a heat exchanger mounted wi thin said housing adapted to have fluid pass between its inlet and outlet and having electrical heating elements for heating the fluid moving through said heat exchanger, a pump having an inlet connected to receive liquid from said reservoir and an outlet communicating with the inlet of said heat exchanger, a fan mounted within said housing adapted to move air over said heat exchanger, electrical drive means within said housing adapted to drive said fan and said pump, the improvement comprising a temperature limiting thermostat controlling energization of said electrical heating elements in response to the temperature of said heat exchanger adjacent its outlet end, and an additional thermostat controlling energization of said pump and fan operating electrical drive means, said last mentioned thermostat being exposed to the air moved over said heat exchanger by said fan and having a thermally conductive connection to said heat exchanger and functioning to energize said electrical drive means when said heat exchanger is above apredetermined temperature value and to deenergize said electrical drive means when the heat exchanger temperature falls below a second predetermined value, the exposure of said additional thermostat to said fan induced air flow serving to narrow the temperature differential between said first and second predetermined temperature values. 

